The dialect is the system SQLAlchemy uses to communicate with various types of DBAPI implementations and databases.
The dialect layer allows us to forget about the database system (e.g. SQLite vs. Postgres) we are using.
Fully tested in CI indicates a version that is tested in the SQLAlchemy CI system and passes all the tests in the test suite.
Normal support indicates that most features should work, but not all versions are tested in the ci configuration so there may be some not supported edge cases. We will try to fix issues that affect these versions.
Best effort indicates that we try to support basic features on them, but most likely there will be unsupported features or errors in some use cases. Pull requests with associated issues may be accepted to continue supporting older versions, which are reviewed on a case-by-case basis.